In the prior art, the same type of seal assembly has been used for a long time for this application, that is one formed by a radial V-shaped spring-loaded lip, which cooperates slidably or directly with the drive shaft or, in more sophisticated seal assemblies, with a radial surface of a sealing screen keyed on the drive shaft. In any case, the seal is exclusively radial and the sealing force exerted by the lip is in direct proportion to the load of the spring and to the state of wear of the lip.
Seal assemblies of the type described have the disadvantage of exerting a progressively deteriorating sealing action as the lip becomes worm This limits the life of this type of seal which is, in addition, sensitive to external contamination and which is therefore protected by an additional seal assembly, known as a dust shield. It is clear that this makes running costs relatively high.